1. Field of the Invention
The present invention relates to muffler assemblies of the type which are used to dampen exhaust noise which is produced by an internal combustion engine. More particularly, the present invention relates to an improved outlet tube and baffle assembly for such a muffler, an improved method of manufacture and to a novel blank which may be used to form an improved outlet tube.
2. Description of the Prior Art
Various types of sound attenuation devices are known in the art which accomplish to some degree the function of silencing the device to which they are attached. One class of such devices which have been found highly effective are the venturi sound suppression devices such as those which are disclosed in U.S. Pat. Nos. 3,672,464 and 4,267,899. A closely related use of venturis is in exhaust ejectors. Many engine air cleaners are typically designed so that particulate matter separated out may be continuously removed or scavenged through a source of negative pressure connected to the air cleaner, and it is known that a suitable negative pressure for this purpose can be obtained by inserting a venturi into an engine exhaust tube and a scavenge tube into the venturi. The venturi and scavenge tube thus form an ejector which may or may not be combined with a muffler. Such an ejector arrangement is shown in U.S. Pat. No. 3,137,553, to Billey. It is also known to combine the functions of muffling and ejection into a single unit, such as is shown in U.S. Pat. No. 3,419,892, issued to Wagner et al. Wagner et al related to a circular venturi which had excellent back pressure and scavenge performance. It required, though, spun or die formed parts. In order to reduce the manufacturing cost of such a device, Schmeichel et al developed an integral fluted tube for sound suppression and exhaust ejection which is disclosed in U.S. Pat. No. 4,580,657. In this device, an exhaust tube was formed of a cylindrical portion with a generally circular inlet and outlet and a constricted portion therebetween which was not circular in cross-section, but rather had an irregular fluted shape.
Recently, a new design has become commercially available from Nelson Industries Inc., which is located in Stoughton, Wisconsin. This design includes a housing; a three-piece outlet tube having a tube portion, a cone portion and a flange portion; an intermediate baffle and support having a bleed hole therein; and a solid baffle member which does not allow sound waves to bleed therethrough. The tube, flange and cone portions are formed from three separate pieces which are apparently welded together during manufacturing. Although this design was an improvement over prior art efforts in terms of manufacture, it is recognized that slight changes in configuration of elements cause different interference patterns of sound waves of the same and different frequencies, and research continues to develop muffler designs having better sound suppression results, reduced back pressure, and/or manufacturing processes which are less costly than those previously known. It is in this sense that the present invention assumes significance relative to the art, and, in this regard, the discussion hereinafter points out the advantages thereof.